如果您只是尝试解析JSON，我建议您使用 JSON 解析库，例如Jackson或Jettison，这是一种更简单的方法。readFile 调用返回一个字符串，它实际上并没有将内容转换为 JavaScript 对象。为了实现这一点，需要对字符串进行JSON.parse或JavaScript eval调用。
如果你真的需要使用 JavaScript 引擎来解析 JSON 并且你使用的是 Java 7，你可以做这样的事情（但我不建议这样做）......
public static void main(final String args[]) throws Exception {
final ScriptEngineManager factory = new ScriptEngineManager();
final ScriptEngine engine = factory.getEngineByName("js");
Object val = null;
Scanner s = null;
try {
s = new Scanner(new File("foo.json"));
s.useDelimiter("\\Z");
engine.getBindings(ScriptContext.GLOBAL_SCOPE).put("json", s.next());
} finally {
if (s != null) {
s.close();
}
}
// The default JavaScript engine in Java 6 does not have JSON.parse
// but eval('(' + json + ')') would work
val = engine.eval("JSON.parse(json)");
// The default value is probably a JavaScript internal object and not very useful
System.out.println(val.getClass() + " = " + val);
// Java 7 uses Rhino 1.7R3 the objects will implement Map or List where appropriate
// So in Java 7 we can turn this into something a little more useable
// This is where Java 6 breaks down, in Java 6 you would have to use the
// sun.org.mozilla.javascript.internal classes to get any useful data
System.out.println(convert(val));
}
@SuppressWarnings("unchecked")
public static Object convert(final Object val) {
if (val instanceof Map) {
final Map<String, Object> result = new HashMap<String, Object>();
for (final Map.Entry<String, Object> entry: ((Map<String, Object>) val).entrySet()) {
result.put(entry.getKey(), convert(entry.getValue()));
}
return result;
} else if (val instanceof List) {
final List<Object> result = new ArrayList<Object>();
for (final Object item: ((List<Object>) val)) {
result.add(convert(item));
}
return result;
}
if (val != null) {
System.out.println(val.getClass() + " = " + val);
}
return val;
}
Java 提供的 JavaScript 引擎排除了 Rhino 提供的一些功能。readFile 函数实际上是由Rhino Shell提供的，而不是引擎实现。Oracle还提供了jrunscript shell可访问的功能，这些功能不在引擎中。
这是一个模仿 Rhino shell readFile 函数并将其添加到 JavaScript 作用域的示例，基于对以下问题的回答：
如何使用 Rhino 在 Javascript 中将 Java 类中的方法添加为全局函数？
public static void main(final String args[]) throws Exception {
final ScriptEngineManager factory = new ScriptEngineManager();
final ScriptEngine engine = factory.getEngineByName("js");
engine.getBindings(ScriptContext.GLOBAL_SCOPE).put("utils", new Utils());
engine.eval("for(var fn in utils) {\r\n" +
" if(typeof utils[fn] === 'function') {\r\n" +
" this[fn] = (function() {\r\n" +
" var method = utils[fn];\r\n" +
" return function() {\r\n" +
" return method.apply(utils,arguments);\r\n" +
" };\r\n" +
" })();\r\n" +
" }\r\n" +
"}");
engine.eval("println(readFile('foo.json'))");
}
static class Utils {
public String readFile(final String fileName) throws FileNotFoundException {
return readFile(fileName, null);
}
public String readFile(final String fileName, final String encoding) throws FileNotFoundException {
Scanner s = null;
try {
s = new Scanner(new File(fileName), (encoding == null)? Charset.defaultCharset().name(): encoding);
s.useDelimiter("\\Z");
return s.next();
} finally {
if (s != null) {
s.close();
}
}
}
}